High altitude platform deployment system

ABSTRACT

A communication system for supporting communications with a target market area. The system includes one or more solar-powered aircraft maintained in, or successively passing through, flight stations or flight patterns around the market area. Each of the aircraft targets limited beamwidth communication antennas on a substantial portion of the target market area. The control system is configured to fly selective flight patterns depending on the aircraft characteristics and the flight conditions. The flight patterns may emphasize high-power-generation patterns such as flying away from the sun for aircraft with wing-mounted solar cells.

The present application is a Continuation application of applicationSer. No. 10/418,738, filed Apr. 17, 2003, which claims priority fromU.S. Provisional Patent Application Ser. No. 60/373,336, filed Apr. 17,2002, both of which are incorporated herein by reference for allpurposes.

BACKGROUND

This invention relates generally to methods and systems of deployingaircraft for use as atmospheric platforms, and more particularly, tocommunication systems employing aircraft as high-altitude platforms.

Among the many types of aircraft (e.g., balloons, dirigibles,traditional fixed wing airplanes, flying wing airplanes andhelicopters), some are capable of high-altitude flight, and some arecapable of hovering or maintaining a relatively small flight station(i.e., a small, laterally and vertically limited airspace) with respectto the ground (“stationkeeping”). A limited number of aircraft have beendeveloped for deployment as high-altitude platforms, such as forcommunication relay systems, which require both high-altitude flying andtight stationkeeping. Such aircraft are preferably solar powered forlong flight duration, and are preferably low-speed aircraft to minimizethe station size.

Operating from high, suborbital altitudes, such aircraft can operate ascommunication relay stations between a large number of ground-based andspace-based stations. However, the limited number of aircraft that cansustain continuous flight for significant lengths of time typically havelimited airspeed ranges, and thus have difficulty in their ability toadapt to changing wind-speeds and weather conditions during flight.Nevertheless, for such aircraft to truly operate as high altitudeplatforms, they must be able to maintain a tight station in a widevariety of wind speeds and weather conditions.

Given the broad range of functions that a long-duration, tightlystationed, suborbital platform has the potential to perform, it isdesirable to design such platforms to be capable of handling largerpayloads and power demands, which typically drain resources that couldotherwise be directed toward less efficient, but more tightlystation-kept flight. Furthermore, because communication system bandwidthand reliability are important, it is preferable that communicationsystems incorporating such aircraft have redundancy and frequency reuse.

In summary, there exists a definite need for methods of maintaining atightly kept station in a variety of weather conditions by along-duration aircraft having flight speed limitations, and a furtherneed for fault tolerant systems that incorporate such aircraft and havehigh bandwidths. Preferably, using such methods, such an aircraft shouldbe able to operate up to very high, suborbital altitudes for longdurations. Importantly, it is desirable for such an aircraft to have thecapability for larger payloads and/or power supply requirements.Furthermore, there exists a need for such an aircraft to be inexpensiveto build and operate and, furthermore, pollution-free. Variousembodiments of the present invention can meet some or all of theseneeds, and provide further, related advantages.

SUMMARY OF THE INVENTION

In various embodiments, the present invention solves some or all of theneeds mentioned above, providing an atmospheric-platform communicationsystem and related methods for providing communication services.

The communication system and method of the invention relate to a targetmarket area, and typically include one or more aircraft. Each aircrafttypically includes one or more communication system antennas configuredfor limited beamwidth communications (transmission and/or reception).The system is typically configured such that the target market area iscontinuously in communication with the antennas of at least oneaircraft.

In some embodiments, the invention features a plurality of aircraft,each of which is assigned to a plurality of flight stations. Eachaircraft's antennas are configured to support communication signals withground-based antennas over a substantial portion of the target marketarea while the aircraft maintains station in its flight station. Theaircraft includes a control system configured to control flight controlsof the aircraft such that the aircraft could be indefinitely maintainedwithin its flight station, preferably through the use of three separateflight patterns designed to minimize ground track. Advantageously, theseembodiments typically allow for high levels of communication bandwidth,while providing for at least some ground-based antennas to beinexpensive and reliable fixed (i.e., non-tracking) antennas.

Likewise, in some embodiments, the control system additionally functionssuch that at least two aircraft are stationed at each flight station.Each day, each of these aircraft alternates between being maintained inthe flight station (and supporting communication signals), and flying ahigh-power-generation flight pattern (such as a pattern that comprisesflying away from the sun) during a portion of the daylight hours.Advantageously, embodiments including this feature will generally beusable at higher latitudes and/or in seasons having shorter days thanembodiments not using partial high-power-generation patterns.

Further embodiments of the invention feature the use of fullhigh-power-generation flight patterns. Generally, these embodimentsprovide additional energy generating efficiency.

Other features and advantages of the invention will become apparent fromthe following detailed description of the preferred embodiments, takenwith the accompanying drawings, which illustrate, by way of example, theprinciples of the invention. The detailed description of particularpreferred embodiments, as set out below to enable one to build and usean embodiment of the invention, are not intended to limit the enumeratedclaims, but rather, they are intended to serve as particular examples ofthe claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an aircraft and a target marketarea as are appropriate for a Communication Relay System embodying thepresent invention.

FIG. 2 is a schematic representation of a first embodiment of aCommunication Relay System of the present invention, using aircraft asdepicted in FIG. 1. The elements of the representation are not drawn inproportion to each other.

FIG. 3 is a schematic representation of variation that can be added tothe first embodiment of the invention, as depicted in FIG. 2. Theelements of the representation are not drawn in proportion to eachother.

FIG. 4 is a schematic representation of a fly-from-sun flight pattern,as flown by the aircraft depicted in FIG. 1, which is used (in part orin its entirety) in some embodiments of the present invention. Theelements of the representation are not drawn in proportion to eachother.

FIG. 5 is a schematic representation of a second embodiment of aCommunication Relay System, which uses parts of the fly-from-sun flightpattern as depicted in FIG. 4. The elements of the representation arenot drawn in proportion to each other.

FIG. 6 is a schematic representation of a third embodiment of aCommunication Relay System, which uses the fly-from-sun flight patternas depicted in FIG. 4. The elements of the representation are not drawnin proportion to each other.

FIG. 7 is a schematic representation of a fourth embodiment of aCommunication Relay System, which uses the fly-from-sun flight patternas depicted in FIG. 4. The elements of the representation are not drawnin proportion to each other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides deployment strategies and relatedcommunication systems having aircraft used as atmospheric platforms.Features and advantages of the invention will become apparent from thefollowing detailed description of the preferred embodiments, taken inconjunction with the accompanying drawings, which illustrate, by way ofexample, the principles of the invention.

With reference to FIGS. 1 and 2, a first communication relay systemembodying the invention includes a (first) plurality of aircraft, suchas the high-altitude aircraft described in U.S. Pat. No. 5,810,284,which is incorporated herein by reference for all purposes. Eachaircraft 101 of the plurality of aircraft is assigned to fly within oneseparate, distinct flight station 103 of a plurality of flight stationsaround a target market area 105, such as a metropolitan area. Thestations are preferably circular or nearly circular, and are preferablylimited with a minimum and maximum altitude.

The flight stations 103 are typically spaced in a pattern that is eithercharacterized by regular spacing, or characterized by spacing thatreflects characteristics of the market area 105 such as communicationdemand levels, obstructions to communication signals, and the like.Preferably, the flight station pattern is a star configuration (asdepicted in FIG. 2), with flight stations at different locations spacedaround the center of the target market area (e.g., the center of acity). Rather than the flight stations being positioned and spaced foraircraft serving adjacent target markets (as might occur in typicalcellular patterns) these flight stations are spaced and positioned foraircraft to serve substantially the same target market area.

The target market area typically has a plurality of ground-basedantennas 107, some of which might be directly connected to communicationsubscribers 109, and some of which might be connected to othercommunications systems such as the Internet 111. Preferably at leastsome of these ground-based antennas are static (non-tracking), limitedbeamwidth antennas that are directed at, and whose beams fullyencompass, a single flight station 103. Static antennas have preferablecost and reliability characteristics, as will be further discussed belowwith respect to a first variation of this embodiment.

Each aircraft 101 includes one or more communication system antennas 121that are configured to support communication signals with (i.e.,broadcast to and/or received from) ground-based antennas 107 throughoutall of, or a substantial portion of, the target market area 105. Inparticular, the substantial portion of the target market area ispreferably all or most of the portion of the target market area that isnot subject to practical limitations (such as obstacles 113, excessivebroadcast angles, excessive broadcast distances, conflicting frequencyuse, or excessive available frequency reuse capacity). Therefore, thesubstantial portion of the target market area is typically the portionof the target market area to which the aircraft is not prevented access,or to which the aircraft is not limited to communication levels belowsome predetermined threshold. As a result, on a plan view of the marketarea, the aircraft are stationed at different angles and radialdistances from the center point of the target market area, and theytrain their antennas toward all of, or at least substantial parts ofthat target market area.

The communication relay system antennas 121 are preferably configuredwith a limited beamwidth. They are preferably targetable toward separatesectors 123 of the target market area, so as to provide frequency reusebetween the aircraft's signals with different sectors of the targetmarket area, and also between the aircraft's signals and signals fromother sources (e.g., other aircraft 101).

The star configuration provides highly reliable, high-bandwidth coverageto a large number of subscribers 109, even in high density market areaswith numerous obstacles 113, such as tall buildings. In particular,relative to the market area there are a large number of aircraft 101that can relay signals, and thus a high total bandwidth can be achieved.Additionally, subscribers that have numerous nearby obstacles willtypically have at least one aircraft with which they can send and/orreceive signals. Furthermore, most subscribers will have two or moreaircraft at different flight stations with which they can maintainsignals, thereby providing them with redundancy and/or increasedbandwidths. This is particularly true for subscribers having more thanone static or dynamically aimable antennas.

For certain ground-based antenna locations, a ground-based antenna 107with a larger-than-normal antenna beamwidth might be necessary tocommunicate with an aircraft 101 at a flight station 103 directly (ornearly) overhead. Alternatively, the ground-based antenna could beactively steerable to track aircraft movement within the flight station.This problem can also be resolved by only communicating with aircraft atflight stations more distant from the ground-based antenna.

Each aircraft 101 preferably includes an automatic control system 125,preferably controlling both the communication system antennas 121 andvarious aircraft flight controls including motor controls and controlsurface controls. Thus, the control system can preferably control boththe flight of the aircraft and the operation of the communication relaysystem. The control system could be a centralized computer system, or adecentralized system having control functions carried out in differentparts of the aircraft. For example, the control system could be locatedin a single computer contained within a pod 127 hanging down from a wingsegment 129 of the aircraft.

In operation, each of the plurality of aircraft 101 fly to, and are thenstationed in, its assigned flight station 103 around the target marketarea 105. While each aircraft is in its flight station, itscommunication system antennas 121 are targeted such that they cansupport communication signals with at least a substantial portion of thetarget market area. The antennas are then operated to support suchcommunication signals.

While the communication system antennas 121 of each aircraft 101 supportcommunication signals with a substantial portion of the target marketarea 105, the control system 125 preferably controls flight controls ofthe aircraft so as to keep the aircraft in the flight station 103, andsuch that it could be maintained in the flight station indefinitely. Inthis first embodiment of the invention, the aircraft power system andthe control system are preferably configured to maintain the aircraft,and operate the communication relay system, for a period of at least aplurality of days, and more preferably for more than a week, or evenmore than a month at a time. Preferably the aircraft replenishes itspower supplies by using solar cells.

The ability of the aircraft 101 to stay within a tight flight station103 depends upon the airspeed range of the aircraft, and upon the truewind speeds at the flight station. To maintain the aircraft in theflight station in varying conditions, where the wind speed can vary upto the maximum flight airspeed of the aircraft, the control system 125is configured to use a plurality of flight patterns to limit the groundtrack of the aircraft, and thereby control the aircraft such that theaircraft could be maintained within its station for an indefinite periodof time (without considering fuel limitations).

Each flight pattern has a range of wind speeds over which it is used.This range varies depending on the aircraft characteristics (e.g., theturning radius, the range of available thrust, the coefficients of liftand drag at various angles of attack, the propensity to slip whileturning, and the like). The minimum size of each flight station iseffectively defined as the largest combined area required to fly threeflight patterns (as described below) throughout their range of windspeeds.

In order to select between the flight patterns, the control systempreferably analyzes various sensor data received either from onboardsensors or from other sensors whose information is communicated to theaircraft. In particular, the sensor data is selected to identify localflight conditions such as the true wind speed (i.e., the velocity of thewind, with respect to the ground, at the altitude at which the aircraftis flying).

The control system preferably receives or calculates a wind speed anddirection, or uses time dependent aircraft positional data that isindicative of wind speed and direction. Based on the wind speedinformation, and based on certain established wind speeds at which theaircraft should change flight patterns, the control system controls theflight pattern of the aircraft.

In particular, if the wind speed is above an established minimumin-place-loiter wind speed, which is typically the minimum airspeed ofthe aircraft, the control system controls the aircraft on a first flightpattern such that it flies directly into the wind. The motor iscontrolled such that the airspeed of the aircraft matches the windspeed, thus causing the aircraft to remain relatively motionless withinthe flight station. Preferably the aircraft is controlled such that itis motionlessly positioned in the middle of the flight station, thusallowing the aircraft room to respond to changes in wind conditions.This is an efficient and preferred pattern, and will be flown most oftenby an aircraft having a wide range of airspeeds.

If the wind speed is above an established minimum zigzag wind speed andbelow the minimum in-place-loiter wind speed, the control systemcontrols the aircraft on a second flight pattern such that it fliesupwind in a zigzag pattern (i.e., alternately left and right of upwind).This pattern is preferably used when the aircraft's lowest airspeed isslightly higher than the wind speed. When the aircraft is at its maximumcrosswind direction (e.g., 30 off of upwind) the aircraft's ground trackwill move to the side and downwind. When the aircraft passes through theupwind direction, its ground track will follow the upwind direction. Theoverall course over the ground of this pattern is a figure-eight shapelaid out across the wind's direction. As the wind speed decreases withrespect to the airspeed, the size of the figure-eights increase. Themotor is preferably controlled to run at or near a minimum levelnecessary for flight. Preferably the aircraft is controlled such thatthe crossing point of the figure-eight is positioned in the middle ofthe flight station to allow the aircraft room to respond to changes inwind conditions.

If the wind speed is below the minimum zigzag wind speed, the controlsystem controls the aircraft on a third flight pattern such that itrepeatedly turns 360 degrees in only one direction. This is the mostefficient pattern for stationkeeping at zero or low wind speeds. At zerowind speed, the bank of the turn will be kept substantially equal, andthe repeatedly turning pattern will be substantially circular. As windspeed increases from zero, the repeatedly turning pattern changes from acircle to a “D” shape, with the straight side of the “D” being flowndirectly into the wind. The motor is preferably controlled to minimizethe ground track, and will typically be run at or near a minimum levelnecessary for flight. Preferably the aircraft is controlled such thatthe pattern is positioned in the middle of the flight station to allowthe aircraft room to respond to changes in wind conditions. Typicallythe minimum zigzag wind speed is established to be the lowest wind speedwhere a repeatedly turning pattern would require a larger flight stationthan a zigzag pattern.

With reference to FIGS. 2 and 3, in a first variation of the firstcommunication relay system embodying the invention, the communicationrelay system is augmented with one or more offset flight stations 141.These offset flight stations each have stationed aircraft 101, and aresignificantly offset from the airspace above or close to the targetmarket area 105. Preferably, the offset flight stations are at an angleof elevation of no more than 45 degrees, or perhaps no more than 20degrees, with respect to the target market area, and are laterally amuch greater distance from the target market area than the firstplurality of flight stations.

The offset flight stations 141 have similarities to a GeostationaryEarth Orbit (GEO) satellite, in that all ground-based antennas 107pointing to the offset flight stations can be fixed, pointing atbasically the same bearing. This is because the antenna's shallow angleof ascent and the aircraft's increased distance from the subscribercombine to more certainly allow a ground-based antenna's beamwidth toencompass a flight station of comparatively larger size relative to anoverhead flight station's size.

The use of offset flight stations allows significant bandwidth reusewhen used in combination with multiple aircraft, such as in a Starconfiguration or in other offset flight stations. Additionally, the useof ground-based antennas that do not need to track the aircraft duringflight offers a number of advantages, including a lower cost to producethe antennas, and a lower cost to install the antennas.

Cost efficient ground-based antenna installation is achieved with theuse of offset flight stations, because the ground-based antennainstallation for an offset flight station is similar to the installationof a geostationary Earth orbit (GEO) antenna, for which a technician cansimply point the antenna at a certain bearing, then adjust antenna formaximum signal strength. Furthermore, additional cost savings can berealized for many customers, because they will not require roof accessto install the antenna. Instead, ground-based antennas can be mounted towindow sills, under eaves, on patios, or possibly looking throughwindows.

The lack of a steering mechanism also reduces the cost and improves thereliability of the antennas. The use of a narrow beamwidth, along withthe low angle of elevation, permits significant angular isolation,allowing significant frequency reuse between aircraft and/or beams froma single aircraft.

It should be noted that use of the offset configuration can be blockedby obstructions such as trees, terrain, or other buildings. Also, lowerelevation angles leads to greater communication distances, which eitherentails the use of stronger signals, with their larger powerrequirements, and/or lower bandwidths. Finally, while the stationkeepingrequirements might allow for larger flight stations, there still mightbe significant stationkeeping requirements that can tax an aircraft'sresources and cause the aircraft to fly in directions that are lessefficient for generating solar power.

In a second communication relay system embodying the invention, theoperation of the first communication relay system is augmented withadditional aircraft that alternate with the above-described, originalaircraft (i.e., the first plurality of aircraft) in relief shifts.Additionally, both the original aircraft and the relief aircraft followflight paths that maximize power generation when the aircraft are notbeing maintained within a flight station.

More particularly, the operation of the first plurality of aircraft,described above with respect to the first embodiment, is augmented witha second plurality of aircraft. Aircraft 101 of the second plurality ofaircraft are stationed in the same flight stations 103 as those of thefirst plurality of aircraft. Aircraft of the second plurality ofaircraft are the same or similar, in both design and operation, to thefirst plurality of aircraft, as described above. This similarityincludes the communication system antennas 121 and the control systems125. Moreover, this similarity includes the functioning of the controlsystems to control flight controls of the aircraft so as to keep theaircraft in the flight station 103, such that they could be maintainedin the flight station indefinitely. As such, the control systems of thesecond plurality of aircraft are also configured to identify localflight conditions, and select between flight patterns such as anin-place-loiter pattern, a zigzag pattern, and a repeatedly turningpattern.

Nevertheless, in this second embodiment of the invention, the controlsystems of the first and second pluralities of aircraft are preferablyconfigured to alternately maintain aircraft of the first and secondpluralities of aircraft in the flight stations during each day. As withthe first embodiment, aircraft preferably are continuously maintained inthe flight stations for a period of at least a plurality of days, andmore preferably for more than a week, or even more than a month at atime, allowing communication relay systems to continuously be operatedin the flight stations over that period of time.

Unlike the first embodiment, during each day of flight, each aircraft ofthe first and second pluralities of aircraft are temporarily freed frombeing maintained in and restricted to its flight station. Preferably,each aircraft is free to leave its flight station for a portion of theday that includes some hours of daylight, and more preferably eachaircraft stationed at a given flight station is free to leave its flightstation to conduct a relatively equal period of high-power-generationflight. Alternatively, each aircraft stationed at a given flight stationis free to leave its flight station for an amount ofhigh-power-generation flight that is in some way proportional inincreased generation to the additional amount of power consumed duringstationkeeping, such as by time spent within the flight station and/ortotal communication activity supported.

Preferably each aircraft of the first and second pluralities of aircraftreplenishes its power supplies by using solar cells whenever appropriatelight is available. During the hours when each aircraft of the first andsecond pluralities of aircraft is free to leave the flight station, thataircraft follows a flight pattern designed to maximize power generation.The pattern preferably allows for the aircraft to return to its flightstation by the time its portion of the day for unconstrained flight isover. However, an alternate variation of this system could allow foraircraft to switch the flight stations at which they are stationedduring their unconstrained flight.

The daily freeing of the aircraft from stationkeeping requirements isadvantageous for several reasons. For example, the flight patternsrequired to maintain a station will often place the aircraft at anorientation that does not provide for maximum illumination of its solarcells, thus reducing power generation. Also, the continuous flightcontrol adjustment and motor settings required in some stationkeepingflight patterns will increase power usage. Additionally, thecommunications activities conducted during stationkeeping will alsorequire additional power usage. Thus, during its relief period, eachaircraft can be allowed to maximize its power generation, both byincreasing the solar cell output and by decreasing the power usage.

With reference to FIG. 4, to maximize its power generation, while awayfrom the flight station each aircraft flies a power-generating patternproviding maximum net power, considering both the solar cell poweroutput and the power required to fly the power-generating pattern. For atypical aircraft having wing-mounted solar cells, the preferred patternis to fly away from the sun during daylight hours, thus providingmaximum illumination to the sloping rear portion of the wings. Since thesize of the solar array is likely to be a dominant cost in producing theaircraft, maximizing power generation from a limited array of cells cansignificantly reduce the cost of manufacturing the aircraft.

For a single plane continuously flying a fly-from-sun pattern in ano-wind condition, the pattern would preferably approximately form alarge D-shaped configuration. In significant wind conditions the D-shapemight be appropriately distorted.

An aircraft 201 flies with the sun 203 behind it all day, adjusting itscourse as the sun move across the sky (relative to the earth) during theday. In particular, during the morning in the northern hemisphere, theaircraft starts at a first location 205 where it flies in a westerlydirection, gradually turning right, toward the north. At approximatelynoon the aircraft passes through a second location 207 where it isflying due north, local time. It continues to turn right, ending the dayflight portion as sunset approaches at a third location 209 where it isflying in an easterly direction.

At night, when the aircraft 201 is flying off of stored energy, itreturns to the first location 205 so that it can again start the dailyflight westbound with the sun directly to its rear. Generally, in theNorthern hemisphere, this will mean that the aircraft flies a backwardD-shaped pattern. Likewise, in the Southern hemisphere a forwardD-shaped pattern is flown. Depending upon the ground speed of theaircraft, such flight patterns can cover hundreds of miles.

With reference to FIG. 5, in the northern hemisphere each aircraft ofthe second embodiment's first and second pluralities of aircraft flies apartial fly-from-sun pattern. In particular, an afternoon aircraft(i.e., an aircraft maintaining the flight station in the afternoon)would be flying west at a sunrise location 301 when the sun rises. Theafternoon aircraft slowly turns toward the north throughout the morningso as to fly away from the sun until half of the daytime (i.e., thedaylight portion of the day) has past. At this point it is flyingsubstantially northward, and it reaches the flight station 303. Throughthis first half of the daytime, the afternoon aircraft has takensignificant advantage of the morning sunlight.

The afternoon aircraft then relieves a morning aircraft that wasmaintaining the flight station 303. The morning aircraft then assumesthe northbound flight pattern, slowly turning east as the sun moves tothe western horizon. At the point of sunset, the morning aircraft is ata sunset location 305, and has taken significant advantage of thesunlight in the second half of the daytime, thereby ensuring a maximumcharge on its energy storage system by the end of the daytime.

After sunset, the morning aircraft returns to the flight station by anyefficient flight path, which might be influenced by the local windspeeds. For example, the evening-generating aircraft could travel duesouth, and then turn to travel due west when reaching a point 307 at thelatitude of the flight station (as depicted). Alternatively, the morningaircraft could fly there in a straight line, or on a smoothly curvedpath to control the morning aircraft's arrival time at the flightstation 303.

Because stationkeeping in the flight station and relaying communicationscan consume more power than steady flight, the morning aircraftpreferably returns to the flight station at a time such that the twoaircraft each stationkeep at the flight station for approximately equallengths of time. Alternatively, if the power requirements are moredemanding during one aircraft's period of stationkeeping, then thearrival could be timed such that other aircraft stationkeeps for arelatively longer period of time to equalize the power usage.

Upon the morning aircraft reaching the flight station, the afternoonaircraft departs the flight station and flies to the sunrise location301, which might have changed from the prior day due to changing windand/or weather conditions, or due to changing aircraft capabilities(e.g., minor system malfunctions or the like). The afternoon aircraftreturns to the sunrise location by any efficient flight path, whichmight be influenced by the local wind speeds. For example, the afternoonaircraft could travel due east to a point due north of the sunriselocation (which might be the pint 307 reached by the morning aircraft),and then turn to travel due south to the sunrise location.Alternatively, the afternoon aircraft could fly to the sunrise locationin a straight line, or upon a smoothly curved path to arrive at sunrise.

The second embodiment provides some of the efficiency associated with afly-from-sun flight pattern, while still giving the advantages of usingrelatively small flight stations that are continually maintained byaircraft. Additionally, aircraft of the second embodiment might be ableto perform other, perhaps less revenue-rich operations, such as imaging,weather monitoring, and emergency communications relay, when they arenot on station. Of course, the second embodiment requires the use ofmore aircraft than the first embodiment, but it can function duringmonths and/or at latitudes where the first embodiment might not be able.Furthermore, variations of this embodiment can include the use of atleast two of the second plurality of aircraft assigned to each flightstation. This allows for each aircraft to use the fly-from-sun flightpattern for approximately two-thirds of each daytime period on theaverage.

In some situations, the use of the second embodiment might only beneeded during low power availability (e.g., during winter when the sunis typically low in the sky and the days are shortest). Thus the firstembodiment could be used for half or two-thirds of the year, and thesecond embodiment for the remainder of the year. Such communicationsystems, using the second embodiment on a part time basis, can share theextra aircraft with other communication systems. For example, theadditional aircraft could be transferred between locations in thenorthern and southern hemispheres to be used in the respective winters.Additionally, in times when neither hemisphere needs to use the secondembodiment, the extra aircraft could be used to relieve aircraft forperiodic maintenance.

The reliability of either the first or second embodiments could beaugmented through variations that use of one or more reserve aircraftmaintained in a flight pattern near the flight stations, and preferablyupwind from the flight stations. Preferably the reserve aircraft aremaintained in the general vicinity through the use of a partial or fullfly-from-sun patterns, ensuring that they have maximum charge in orderto relieve any aircraft on station when necessary.

With Reference to FIG. 6, a third communication relay system embodyingthe invention includes a plurality of aircraft, each flying a fullfly-from-sun pattern that is offset from the other fly-from-sunpatterns. In particular, a first pattern 401 is located such that itsassociated aircraft is stationed within operating communications rangeof the target market area 403 at sunrise, and for a period of timebefore and after sunrise. Additional patterns 405 are located so as tocoordinate each aircraft's arrival in the station such that eachaircraft consecutively takes over as the active communication relaysystem, until the aircraft in a final pattern 407 takes over at a timebefore sunset, and continues for a period of time after sunset.

Throughout the time between sunset and sunrise, the communication relayduties are then passed back through the series of aircraft until theyare again assumed by the aircraft flying the first pattern 401.Alternatively, additional aircraft could be flying in additionalfly-from-sun patterns that brings them close to the target market areaat various times during the evening.

Thus, each aircraft is in the vicinity of the target market area at adifferent time. Each aircraft will be traveling in a different directionin its time in the vicinity of the target market area (as is shown byoverlapping aircraft images in the figure), and thus each aircraft'scontrol system must target its antennas appropriately.

The station size is typically configured based on the number of aircraftand the characteristics of their fly-from-sun flight patterns. Note thatthis size, like the travel range of the fly-from-sun flight pattern, isdependent upon the wind speed and direction at the station. In the eventthat the wind doesn't cooperate, it may be possible to fly sub-optimalflight paths to put the aircraft in the stations at the appropriate.These sub-optimal flight patterns could include the half fly-from-sunpattern described above with respect to the second embodiment.

Unlike the first two embodiments, the third embodiment does nottypically have tight flight stations. Instead, it is configured withbroad flight stations so that at least one aircraft is in effectivecommunications range at all times. Actively tracking, limited beamwidth,ground-based antennas will generally be used for this embodiment, as theantennas will have to both follow moving aircraft, and periodicallyre-target on new aircraft. Alternatively, significantly wider beamwidth,ground-based antennas or omnidirectional antennas could be used.

This embodiment allows for lower cost aircraft to be used. Inparticular, cost savings can be achieved by using less-efficient solarcells on an aircraft configured to provide service over a given area.Additionally, this embodiment has the potential to allow a givenaircraft to be used at higher latitudes than could otherwise be handledby a tight stationkeeping embodiment. The embodiment can be used inhigher latitudes because the solar cells can get more power from the sunduring their greater exposure to the sun.

Furthermore, in this configuration (and other configurations whereaircraft depart from their flight stations) it may be possible toperform other, less revenue rich operations, such as imaging, weathermonitoring, and emergency communications relay, when the aircraft arenot on station. Furthermore, as depicted in FIG. 7, if more than onetarget market area 501 is in the same vicinity, some aircraft may haveflight patterns 503 located to serve multiple service areas during aday, reducing the total number of aircraft needed per service area.Furthermore, if a larger number of service areas are in the sameproximity, ground track variation (caused by weather and windconditions) can be adapted to by assigning whichever aircraft is mostefficiently available to serve each area sharing the group of aircraft.

With reference to FIG. 4, a fourth communication relay system embodyingthe invention can be formed by a single aircraft 201 that operates witha high-power-generation flight pattern. As depicted in the figure, underthe direction of its control system, the aircraft preferably flies afly-from-sun pattern. The pattern is preferably positioned such that itsextreme ends are approximately equidistant from the target market area,such that it is positioned to maximize the antennas' communication withthe target market area. Alternatively, the pattern can be shifted tomaximize communications during times of day when maximum bandwidths areneeded.

The communication relay system includes ground-based antennas thatactively tracking, limited beamwidth antennas. Alternatively,significantly wider beamwidth ground-based antennas or omnidirectionalantennas could be used.

In a variation of this embodiment, limited, and/or partial fly-from-sunpatterns could be used to lessen the distance that the aircraft fliesfrom the target market area. For example, in one limited fly-from-sunpattern, the aircraft could begin by maintaining a station to the eastof the target market area during the night. Soon after sunrise, theaircraft flies to the west, substantially away from the sun. It does sountil it reaches its eastern station, where it stays most of theremainder of the day. In the afternoon, it flies from its westernstation back to the eastern station, again flying substantially awayfrom the sun. Both the western and the eastern stations are chosen to bewithin a range of the target market area such that the aircraft canservice that area at all times.

Depending on the target market area and the aircraft mission, theeastern and western stations could be only a few miles apart, or theycould be 100 miles or more apart. The further apart they are, the morebenefit that is gained from the fly-from-sun legs. However, the furtherapart they are, the more the communication is limited between theaircraft and the target market area. For example, ground antennascapable of tracking the aircraft position might be required, or areduced area of coverage might result from this flight pattern. Inpractice, the distance between the two stations is chosen to optimizethe total system performance.

In other variations, the limited fly-from-sun pattern might be morecomplex than just an east-west leg pair. For example, in the highnorthern latitudes during the summer, the sun is almost always above thehorizon, but at a low elevation angle. In such a situation, the aircraftcan fly several legs resulting in it circling the target area once perday. It would fly part way around the circle, stationkeep for a while,fly further around the circle, station keep, and so on. In the northernhemisphere the aircraft flies around the circle clockwise with each legin a direction substantially away from the sun. The diameter of thecircle is preferably chosen to optimize the system. Larger circlesresult in increased performance, but they make servicing the target areamore difficult due to increased transmission distances and/or increasedground-based antenna tracking difficulties.

In high northern latitudes during the winter, the limited Fly-From-Sunpattern can take the form of a reduced size D loop. This is similar tothe “D” loop made by the full fly-from-sun pattern, but it is madesmaller by having the aircraft intersperse station keeping periods oftime amidst fly-from-sun periods. The diameter of the “D” loop is againchosen to optimize the system performance. Bigger loops result inincreased aircraft performance, but at the expense of making the targetarea more difficult to acquire and maintain.

The preferred embodiments of the invention include methods of deployingone or more aircraft so as to enable their use as high altitudeplatforms, and the resulting high-altitude platform deployment systems.While a particular form of the invention is illustrated and described,it will be apparent that various modifications can be made withoutdeparting from the spirit and scope of the invention. For example, whilethe embodiments all describe communication relay systems, the inventionis also applicable for other uses of high altitude platforms. Thus,although the invention is described in detail with reference only to thepreferred embodiment, those having ordinary skill in the art willappreciate that various modifications can be made without departing fromthe invention.

1. A method of establishing a communication system for a target marketarea, comprising: stationing each of a plurality of aircraft in separateflight stations of a plurality of flight stations around the targetmarket area, wherein each aircraft has one or more communication systemantennas configured with a limited beamwidth; while each aircraft of theplurality of aircraft is in its flight station, targeting the one ormore communication system antennas of that aircraft such that theysupport communication signals with a substantial portion of the targetmarket area; and while the communication system antennas of eachaircraft support communication signals with a substantial portion of thetarget market area, controlling flight controls of that aircraft suchthat the aircraft could be indefinitely maintained within its flightstation.
 2. A communication system for a target market area, comprisinga plurality of aircraft, each of which is for use in separate flightstations of a plurality of flight stations around the target marketarea, each aircraft including: one or more communication system antennasconfigured with a limited beamwidth, and further configured to supportcommunication signals with a substantial portion of the target marketarea while the aircraft is in its flight station; and a control systemconfigured to control flight controls of that aircraft such that theaircraft could be indefinitely maintained within its station while thecommunication system antennas of each aircraft support communicationsignals with a substantial portion of the target market area.
 3. Acommunication system for a target market area, comprising a firstaircraft and a second aircraft for use in a flight station around thetarget market area, each aircraft including: one or more communicationsystem antennas configured with a limited beamwidth, and furtherconfigured to support communication signals with a substantial portionof the target market area while the aircraft is in the flight station;and a control system configured to maintain the aircraft within thestation during a portion of each day of flight, and to fly ahigh-power-generation pattern outside of the station during a portion ofthe daylight hours of each day of flight, wherein the control system isfurther configured to control flight controls of the aircraft such thatthe aircraft could be indefinitely maintained within the station whilethe aircraft is being maintained within the station; wherein the controlsystem is further configured to coordinate with the control system ofthe other aircraft such that at least one aircraft is maintained withinthe station at all times during each day of flight.
 4. A communicationsystem for a target market area, comprising: a solar powered aircraftconfigured to continuously fly a high-power-generation pattern, theaircraft including one or more communication system antennas with alimited beamwidth, the antennas being configured to supportcommunication signals with a plurality of ground antennas in asubstantial portion of the target market area; and a ground antenna inthe target market area configured to track the aircraft, and furtherconfigured to support communication signals with the antennas of theaircraft.
 5. A communication system for a target market area having adesignated flight station, comprising a plurality of aircraft, each ofwhich is for use in separate flight patterns of a plurality of flightpatterns located around the target market area and passing through theflight station, each aircraft including: one or more communicationsystem antennas configured with a limited beamwidth, and furtherconfigured to support communication signals with a substantial portionof the target market area while the aircraft is passing through theflight station; and a control system configured to control flightcontrols of that aircraft such that the aircraft flies ahigh-power-generation flight pattern, wherein the control system isconfigured to coordinate with the control systems of the other aircraftto assure that each aircraft's departure form the flight station isslightly preceded by another aircraft's arrival in the flight station.6. A communication system for a target market area, comprising: anaircraft configured with one or more communication system antennas and acontrol system; wherein the one or more communication system antennasare configured with a limited beamwidth, and are further configured tosupport communication signals with a substantial portion of the targetmarket area; and wherein the control system is configured to controlflight controls of that aircraft such that the aircraft flies ahigh-power-generation flight pattern positioned to maximize the antennascommunication with the target market area.